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PERLVAR(1)	       Perl Programmers Reference Guide 	    PERLVAR(1)

       perlvar - Perl predefined variables

       Predefined Names

       The following names have special meaning to Perl.  Most punctuation
       names have reasonable mnemonics, or analogs in the shells.  Neverthe
       less, if you wish to use long variable names, you need only say

	   use English;

       at the top of your program. This aliases all the short names to the
       long names in the current package. Some even have medium names, gener
       ally borrowed from awk. In general, its best to use the

	   use English -no_match_vars;

       invocation if you dont need $PREMATCH, $MATCH, or $POSTMATCH, as it
       avoids a certain performance hit with the use of regular expressions.
       See English.

       Variables that depend on the currently selected filehandle may be set
       by calling an appropriate object method on the IO::Handle object,
       although this is less efficient than using the regular built-in vari
       ables. (Summary lines below for this contain the word HANDLE.) First
       you must say

	   use IO::Handle;

       after which you may use either

	   method HANDLE EXPR

       or more safely,


       Each method returns the old value of the IO::Handle attribute.  The
       methods each take an optional EXPR, which, if supplied, specifies the
       new value for the IO::Handle attribute in question.  If not supplied,
       most methods do nothing to the current value--except for autoflush(),
       which will assume a 1 for you, just to be different.

       Because loading in the IO::Handle class is an expensive operation, you
       should learn how to use the regular built-in variables.

       A few of these variables are considered "read-only".  This means that
       if you try to assign to this variable, either directly or indirectly
       through a reference, youll raise a run-time exception.

       You should be very careful when modifying the default values of most
       special variables described in this document. In most cases you want to
       localize these variables before changing them, since if you dont, the
       change may affect other modules which rely on the default values of the
       special variables that you have changed. This is one of the correct
       ways to read the whole file at once:

	   open my $fh, "foo" or die $!;
	   local $/; # enable localized slurp mode
	   my $content = <$fh>;
	   close $fh;

       But the following code is quite bad:

	   open my $fh, "foo" or die $!;
	   undef $/; # enable slurp mode
	   my $content = <$fh>;
	   close $fh;

       since some other module, may want to read data from some file in the
       default "line mode", so if the code we have just presented has been
       executed, the global value of $/ is now changed for any other code run
       ning inside the same Perl interpreter.

       Usually when a variable is localized you want to make sure that this
       change affects the shortest scope possible. So unless you are already
       inside some short "{}" block, you should create one yourself. For exam

	   my $content = ;
	   open my $fh, "foo" or die $!;
	       local $/;
	       $content = <$fh>;
	   close $fh;

       Here is an example of how your own code can go broken:

	   for (1..5){
	       print "$_ ";
	   sub nasty_break {
	       $_ = 5;
	       # do something with $_

       You probably expect this code to print:

	   1 2 3 4 5

       but instead you get:

	   5 5 5 5 5

       Why? Because nasty_break() modifies $_ without localizing it first. The
       fix is to add local():

	       local $_ = 5;

       Its easy to notice the problem in such a short example, but in more
       complicated code you are looking for trouble if you dont localize
       changes to the special variables.

       The following list is ordered by scalar variables first, then the
       arrays, then the hashes.

       $_      The default input and pattern-searching space.  The following
	       pairs are equivalent:

		   while (<>) {...}    # equivalent only in while!
		   while (defined($_ = <>)) {...}

		   $_ =~ /^Subject:/

		   $_ =~ tr/a-z/A-Z/


	       Here are the places where Perl will assume $_ even if you dont
	       use it:

	       *  Various unary functions, including functions like ord() and
		  int(), as well as the all file tests ("-f", "-d") except for
		  "-t", which defaults to STDIN.

	       *  Various list functions like print() and unlink().

	       *  The pattern matching operations "m//", "s///", and "tr///"
		  when used without an "=~" operator.

	       *  The default iterator variable in a "foreach" loop if no
		  other variable is supplied.

	       *  The implicit iterator variable in the grep() and map() func

	       *  The default place to put an input record when a "" oper
		  ations result is tested by itself as the sole criterion of
		  a "while" test.  Outside a "while" test, this will not hap

	       (Mnemonic: underline is understood in certain operations.)

       $b      Special package variables when using sort(), see "sort" in
	       perlfunc.  Because of this specialness $a and $b dont need to
	       be declared (using use vars, or our()) even when using the
	       "strict vars" pragma.  Dont lexicalize them with "my $a" or
	       "my $b" if you want to be able to use them in the sort() com
	       parison block or function.

	       Contains the subpattern from the corresponding set of capturing
	       parentheses from the last pattern match, not counting patterns
	       matched in nested blocks that have been exited already.
	       (Mnemonic: like \digits.)  These variables are all read-only
	       and dynamically scoped to the current BLOCK.

       $&      The string matched by the last successful pattern match (not
	       counting any matches hidden within a BLOCK or eval() enclosed
	       by the current BLOCK).  (Mnemonic: like & in some editors.)
	       This variable is read-only and dynamically scoped to the cur
	       rent BLOCK.

	       The use of this variable anywhere in a program imposes a con
	       siderable performance penalty on all regular expression
	       matches.  See "BUGS".

       $      The string preceding whatever was matched by the last success
	       ful pattern match (not counting any matches hidden within a
	       BLOCK or eval enclosed by the current BLOCK).  (Mnemonic: ""
	       often precedes a quoted string.)  This variable is read-only.

	       The use of this variable anywhere in a program imposes a con
	       siderable performance penalty on all regular expression
	       matches.  See "BUGS".

       $      The string following whatever was matched by the last success
	       ful pattern match (not counting any matches hidden within a
	       BLOCK or eval() enclosed by the current BLOCK).	(Mnemonic: ""
	       often follows a quoted string.)	Example:

		   local $_ = abcdefghi;
		   print "$:$&:$\n";	     # prints abc:def:ghi

	       This variable is read-only and dynamically scoped to the cur
	       rent BLOCK.

	       The use of this variable anywhere in a program imposes a con
	       siderable performance penalty on all regular expression
	       matches.  See "BUGS".

       $+      The text matched by the last bracket of the last successful
	       search pattern.	This is useful if you dont know which one of
	       a set of alternative patterns matched. For example:

		   /Version: (.*)|Revision: (.*)/ && ($rev = $+);

	       (Mnemonic: be positive and forward looking.)  This variable is
	       read-only and dynamically scoped to the current BLOCK.

       $^N     The text matched by the used group most-recently closed (i.e.
	       the group with the rightmost closing parenthesis) of the last
	       successful search pattern.  (Mnemonic: the (possibly) Nested
	       parenthesis that most recently closed.)

	       This is primarily used inside "(?{...})" blocks for examining
	       text recently matched. For example, to effectively capture text
	       to a variable (in addition to $1, $2, etc.), replace "(...)"

		    (?:(...)(?{ $var = $^N }))

	       By setting and then using $var in this way relieves you from
	       having to worry about exactly which numbered set of parentheses
	       they are.

	       This variable is dynamically scoped to the current BLOCK.

       @+      This array holds the offsets of the ends of the last successful
	       submatches in the currently active dynamic scope.  $+[0] is the
	       offset into the string of the end of the entire match.  This is
	       the same value as what the "pos" function returns when called
	       on the variable that was matched against.  The nth element of
	       this array holds the offset of the nth submatch, so $+[1] is
	       the offset past where $1 ends, $+[2] the offset past where $2
	       ends, and so on.  You can use $#+ to determine how many sub
	       groups were in the last successful match.  See the examples
	       given for the "@-" variable.

       $*      Set to a non-zero integer value to do multi-line matching
	       within a string, 0 (or undefined) to tell Perl that it can
	       assume that strings contain a single line, for the purpose of
	       optimizing pattern matches.  Pattern matches on strings con
	       taining multiple newlines can produce confusing results when $*
	       is 0 or undefined. Default is undefined.  (Mnemonic: * matches
	       multiple things.) This variable influences the interpretation
	       of only "^" and "$". A literal newline can be searched for even
	       when "$* == 0".

	       Use of $* is deprecated in modern Perl, supplanted by the "/s"
	       and "/m" modifiers on pattern matching.

	       Assigning a non-numerical value to $* triggers a warning (and
	       makes $* act if "$* == 0"), while assigning a numerical value
	       to $* makes that an implicit "int" is applied on the value.

       $.      Current line number for the last filehandle accessed.

	       Each filehandle in Perl counts the number of lines that have
	       been read from it.  (Depending on the value of $/, Perls idea
	       of what constitutes a line may not match yours.)  When a line
	       is read from a filehandle (via readline() or "<>"), or when
	       tell() or seek() is called on it, $. becomes an alias to the
	       line counter for that filehandle.

	       You can adjust the counter by assigning to $., but this will
	       not actually move the seek pointer.  Localizing $. will not
	       localize the filehandles line count.  Instead, it will local
	       ize perls notion of which filehandle $. is currently aliased

	       $. is reset when the filehandle is closed, but not when an open
	       filehandle is reopened without an intervening close().  For
	       more details, see "I/O Operators" in perlop.  Because "<>"
	       never does an explicit close, line numbers increase across ARGV
	       files (but see examples in "eof" in perlfunc).

	       You can also use "HANDLE->input_line_number(EXPR)" to access
	       the line counter for a given filehandle without having to worry
	       about which handle you last accessed.

	       (Mnemonic: many programs use "." to mean the current line num

       $/      The input record separator, newline by default.	This influ
	       ences Perls idea of what a "line" is.  Works like awks RS
	       variable, including treating empty lines as a terminator if set
	       to the null string.  (An empty line cannot contain any spaces
	       or tabs.)  You may set it to a multi-character string to match
	       a multi-character terminator, or to "undef" to read through the
	       end of file.  Setting it to "\n\n" means something slightly
	       different than setting to "", if the file contains consecutive
	       empty lines.  Setting to "" will treat two or more consecutive
	       empty lines as a single empty line.  Setting to "\n\n" will
	       blindly assume that the next input character belongs to the
	       next paragraph, even if its a newline.  (Mnemonic: / delimits
	       line boundaries when quoting poetry.)

		   local $/;	       # enable "slurp" mode
		   local $_ = ;    # whole file now here
		   s/\n[ \t]+/ /g;

	       Remember: the value of $/ is a string, not a regex.  awk has to
	       be better for something. :-)

	       Setting $/ to a reference to an integer, scalar containing an
	       integer, or scalar thats convertible to an integer will
	       attempt to read records instead of lines, with the maximum
	       record size being the referenced integer.  So this:

		   local $/ = \32768; # or \"32768", or \$var_containing_32768
		   open my $fh, $myfile or die $!;
		   local $_ = <$fh>;

	       will read a record of no more than 32768 bytes from FILE.  If
	       youre not reading from a record-oriented file (or your OS
	       doesnt have record-oriented files), then youll likely get a
	       full chunk of data with every read.  If a record is larger than
	       the record size youve set, youll get the record back in

	       On VMS, record reads are done with the equivalent of "sysread",
	       so its best not to mix record and non-record reads on the same
	       file.  (This is unlikely to be a problem, because any file
	       youd want to read in record mode is probably unusable in line
	       mode.)  Non-VMS systems do normal I/O, so its safe to mix
	       record and non-record reads of a file.

	       See also "Newlines" in perlport.  Also see $..

       $|      If set to nonzero, forces a flush right away and after every
	       write or print on the currently selected output channel.
	       Default is 0 (regardless of whether the channel is really
	       buffered by the system or not; $| tells you only whether youve
	       asked Perl explicitly to flush after each write).  STDOUT will
	       typically be line buffered if output is to the terminal and
	       block buffered otherwise.  Setting this variable is useful pri
	       marily when you are outputting to a pipe or socket, such as
	       when you are running a Perl program under rsh and want to see
	       the output as its happening.  This has no effect on input
	       buffering.  See "getc" in perlfunc for that.  (Mnemonic: when
	       you want your pipes to be piping hot.)

       IO::Handle->output_field_separator EXPR
       $,      The output field separator for the print operator.  If defined,
	       this value is printed between each of prints arguments.
	       Default is "undef".  (Mnemonic: what is printed when there is a
	       "," in your print statement.)

       IO::Handle->output_record_separator EXPR
       $\      The output record separator for the print operator.  If
	       defined, this value is printed after the last of prints argu
	       ments.  Default is "undef".  (Mnemonic: you set "$\" instead of
	       adding "\n" at the end of the print.  Also, its just like $/,
	       but its what you get "back" from Perl.)

       $"      This is like $, except that it applies to array and slice val
	       ues interpolated into a double-quoted string (or similar inter
	       preted string).	Default is a space.  (Mnemonic: obvious, I

       $;      The subscript separator for multidimensional array emulation.
	       If you refer to a hash element as


	       it really means

		   $foo{join($;, $a, $b, $c)}

	       But dont put

		   @foo{$a,$b,$c}      # a slice--note the @

	       which means


	       Default is "\034", the same as SUBSEP in awk.  If your keys
	       contain binary data there might not be any safe value for $;.
	       (Mnemonic: comma (the syntactic subscript separator) is a
	       semi-semicolon.	Yeah, I know, its pretty lame, but $, is
	       already taken for something more important.)

	       Consider using "real" multidimensional arrays as described in

       $#      The output format for printed numbers.  This variable is a
	       half-hearted attempt to emulate awks OFMT variable.  There are
	       times, however, when awk and Perl have differing notions of
	       what counts as numeric.	The initial value is "%.ng", where n
	       is the value of the macro DBL_DIG from your systems float.h.
	       This is different from awks default OFMT setting of "%.6g", so
	       you need to set $# explicitly to get awks value.  (Mnemonic: #
	       is the number sign.)

	       Use of $# is deprecated.

       $%      The current page number of the currently selected output chan
	       nel.  Used with formats.  (Mnemonic: % is page number in

       $=      The current page length (printable lines) of the currently
	       selected output channel.  Default is 60.  Used with formats.
	       (Mnemonic: = has horizontal lines.)

       $-      The number of lines left on the page of the currently selected
	       output channel.	Used with formats.  (Mnemonic: lines_on_page -

       @-      $-[0] is the offset of the start of the last successful match.
	       "$-["n"]" is the offset of the start of the substring matched
	       by n-th subpattern, or undef if the subpattern did not match.

	       Thus after a match against $_, $& coincides with "substr $_,
	       $-[0], $+[0] - $-[0]".  Similarly, $n coincides with "substr
	       $_, $-[n], $+[n] - $-[n]" if "$-[n]" is defined, and $+ coin
	       cides with "substr $_, $-[$#-], $+[$#-] - $-[$#-]".  One can
	       use "$#-" to find the last matched subgroup in the last suc
	       cessful match.  Contrast with $#+, the number of subgroups in
	       the regular expression.	Compare with "@+".

	       This array holds the offsets of the beginnings of the last suc
	       cessful submatches in the currently active dynamic scope.
	       "$-[0]" is the offset into the string of the beginning of the
	       entire match.  The nth element of this array holds the offset
	       of the nth submatch, so "$-[1]" is the offset where $1 begins,
	       "$-[2]" the offset where $2 begins, and so on.

	       After a match against some variable $var:

	       $ is the same as "substr($var, 0, $-[0])"
	       $& is the same as "substr($var, $-[0], $+[0] - $-[0])"
	       $ is the same as "substr($var, $+[0])"
	       $1 is the same as "substr($var, $-[1], $+[1] - $-[1])"
	       $2 is the same as "substr($var, $-[2], $+[2] - $-[2])"
	       $3 is the same as "substr($var, $-[3], $+[3] - $-[3])"
       $~      The name of the current report format for the currently
	       selected output channel.  Default is the name of the filehan
	       dle.  (Mnemonic: brother to $^.)

       $^      The name of the current top-of-page format for the currently
	       selected output channel.  Default is the name of the filehandle
	       with _TOP appended.  (Mnemonic: points to top of page.)

       IO::Handle->format_line_break_characters EXPR
       $:      The current set of characters after which a string may be bro
	       ken to fill continuation fields (starting with ^) in a format.
	       Default is " \n-", to break on whitespace or hyphens.
	       (Mnemonic: a "colon" in poetry is a part of a line.)

       IO::Handle->format_formfeed EXPR
       $^L     What formats output as a form feed.  Default is \f.

       $^A     The current value of the write() accumulator for format()
	       lines.  A format contains formline() calls that put their
	       result into $^A.  After calling its format, write() prints out
	       the contents of $^A and empties.  So you never really see the
	       contents of $^A unless you call formline() yourself and then
	       look at it.  See perlform and "formline()" in perlfunc.

       $?      The status returned by the last pipe close, backtick () com
	       mand, successful call to wait() or waitpid(), or from the sys
	       tem() operator.	This is just the 16-bit status word returned
	       by the wait() system call (or else is made up to look like it).
	       Thus, the exit value of the subprocess is really ("$? >> 8"),
	       and "$? & 127" gives which signal, if any, the process died
	       from, and "$? & 128" reports whether there was a core dump.
	       (Mnemonic: similar to sh and ksh.)

	       Additionally, if the "h_errno" variable is supported in C, its
	       value is returned via $? if any "gethost*()" function fails.

	       If you have installed a signal handler for "SIGCHLD", the value
	       of $? will usually be wrong outside that handler.

	       Inside an "END" subroutine $? contains the value that is going
	       to be given to "exit()".  You can modify $? in an "END" subrou
	       tine to change the exit status of your program.	For example:

		   END {
		       $? = 1 if $? == 255;  # die would make it 255

	       Under VMS, the pragma "use vmsish status" makes $? reflect
	       the actual VMS exit status, instead of the default emulation of
	       POSIX status; see "$?" in perlvms for details.

	       Also see "Error Indicators".

	       The object reference to the Encode object that is used to con
	       vert the source code to Unicode.  Thanks to this variable your
	       perl script does not have to be written in UTF-8.  Default is
	       undef.  The direct manipulation of this variable is highly dis
	       couraged.  See encoding for more details.

       $!      If used numerically, yields the current value of the C "errno"
	       variable, or in other words, if a system or library call fails,
	       it sets this variable.  This means that the value of $! is
	       meaningful only immediately after a failure:

		   if (open(FH, $filename)) {
		       # Here $! is meaningless.
		   } else {
		       # ONLY here is $! meaningful.
		       # Already here $! might be meaningless.
		   # Since here we might have either success or failure,
		   # here $! is meaningless.

	       In the above meaningless stands for anything: zero, non-zero,
	       "undef".  A successful system or library call does not set the
	       variable to zero.

	       If used as a string, yields the corresponding system error
	       string.	You can assign a number to $! to set errno if, for
	       instance, you want "$!" to return the string for error n, or
	       you want to set the exit value for the die() operator.
	       (Mnemonic: What just went bang?)

	       Also see "Error Indicators".

       %!      Each element of "%!" has a true value only if $! is set to that
	       value.  For example, $!{ENOENT} is true if and only if the cur
	       rent value of $! is "ENOENT"; that is, if the most recent error
	       was "No such file or directory" (or its moral equivalent: not
	       all operating systems give that exact error, and certainly not
	       all languages).	To check if a particular key is meaningful on
	       your system, use "exists $!{the_key}"; for a list of legal
	       keys, use "keys %!".  See Errno for more information, and also
	       see above for the validity of $!.

       $^E     Error information specific to the current operating system.  At
	       the moment, this differs from $! under only VMS, OS/2, and
	       Win32 (and for MacPerl).  On all other platforms, $^E is always
	       just the same as $!.

	       Under VMS, $^E provides the VMS status value from the last sys
	       tem error.  This is more specific information about the last
	       system error than that provided by $!.  This is particularly
	       important when $! is set to EVMSERR.

	       Under OS/2, $^E is set to the error code of the last call to
	       OS/2 API either via CRT, or directly from perl.

	       Under Win32, $^E always returns the last error information
	       reported by the Win32 call "GetLastError()" which describes the
	       last error from within the Win32 API.  Most Win32-specific code
	       will report errors via $^E.  ANSI C and Unix-like calls set
	       "errno" and so most portable Perl code will report errors via

	       Caveats mentioned in the description of $! generally apply to
	       $^E, also.  (Mnemonic: Extra error explanation.)

	       Also see "Error Indicators".

       $@      The Perl syntax error message from the last eval() operator.
	       If $@ is the null string, the last eval() parsed and executed
	       correctly (although the operations you invoked may have failed
	       in the normal fashion).	(Mnemonic: Where was the syntax error

	       Warning messages are not collected in this variable.  You can,
	       however, set up a routine to process warnings by setting
	       $SIG{__WARN__} as described below.

	       Also see "Error Indicators".

       $$      The process number of the Perl running this script.  You should
	       consider this variable read-only, although it will be altered
	       across fork() calls.  (Mnemonic: same as shells.)

	       Note for Linux users: on Linux, the C functions "getpid()" and
	       "getppid()" return different values from different threads. In
	       order to be portable, this behavior is not reflected by $$,
	       whose value remains consistent across threads. If you want to
	       call the underlying "getpid()", you may use the CPAN module

       $<      The real uid of this process.  (Mnemonic: its the uid you came
	       from, if youre running setuid.)	You can change both the real
	       uid and the effective uid at the same time by using
	       POSIX::setuid().  Since changes to $< require a system call,
	       check $! after a change attempt to detect any possible errors.

       $>      The effective uid of this process.  Example:

		   $< = $>;	       # set real to effective uid
		   ($<,$>) = ($>,$<);  # swap real and effective uid

	       You can change both the effective uid and the real uid at the
	       same time by using POSIX::setuid().  Changes to $> require a
	       check to $!  to detect any possible errors after an attempted

	       (Mnemonic: its the uid you went to, if youre running setuid.)
	       $< and $> can be swapped only on machines supporting

       $(      The real gid of this process.  If you are on a machine that
	       supports membership in multiple groups simultaneously, gives a
	       space separated list of groups you are in.  The first number is
	       the one returned by getgid(), and the subsequent ones by get
	       groups(), one of which may be the same as the first number.

	       However, a value assigned to $( must be a single number used to
	       set the real gid.  So the value given by $( should not be
	       assigned back to $( without being forced numeric, such as by
	       adding zero.

	       You can change both the real gid and the effective gid at the
	       same time by using POSIX::setgid().  Changes to $( require a
	       check to $!  to detect any possible errors after an attempted

	       (Mnemonic: parentheses are used to group things.  The real gid
	       is the group you left, if youre running setgid.)

       $)      The effective gid of this process.  If you are on a machine
	       that supports membership in multiple groups simultaneously,
	       gives a space separated list of groups you are in.  The first
	       number is the one returned by getegid(), and the subsequent
	       ones by getgroups(), one of which may be the same as the first

	       Similarly, a value assigned to $) must also be a space-sepa
	       rated list of numbers.  The first number sets the effective
	       gid, and the rest (if any) are passed to setgroups().  To get
	       the effect of an empty list for setgroups(), just repeat the
	       new effective gid; that is, to force an effective gid of 5 and
	       an effectively empty setgroups() list, say " $) = "5 5" ".

	       You can change both the effective gid and the real gid at the
	       same time by using POSIX::setgid() (use only a single numeric
	       argument).  Changes to $) require a check to $! to detect any
	       possible errors after an attempted change.

	       (Mnemonic: parentheses are used to group things.  The effective
	       gid is the group thats right for you, if youre running set

	       $<, $>, $( and $) can be set only on machines that support the
	       corresponding set[re][ug]id() routine.  $( and $) can be
	       swapped only on machines supporting setregid().

       $0      Contains the name of the program being executed.

	       On some (read: not all) operating systems assigning to $0 modi
	       fies the argument area that the "ps" program sees.  On some
	       platforms you may have to use special "ps" options or a differ
	       ent "ps" to see the changes.  Modifying the $0 is more useful
	       as a way of indicating the current program state than it is for
	       hiding the program youre running.  (Mnemonic: same as sh and

	       Note that there are platform specific limitations on the maxi
	       mum length of $0.  In the most extreme case it may be limited
	       to the space occupied by the original $0.

	       In some platforms there may be arbitrary amount of padding, for
	       example space characters, after the modified name as shown by
	       "ps".  In some platforms this padding may extend all the way to
	       the original length of the argument area, no matter what you do
	       (this is the case for example with Linux 2.2).

	       Note for BSD users: setting $0 does not completely remove
	       "perl" from the ps(1) output.  For example, setting $0 to "foo
	       bar" may result in "perl: foobar (perl)" (whether both the
	       "perl: " prefix and the " (perl)" suffix are shown depends on
	       your exact BSD variant and version).  This is an operating sys
	       tem feature, Perl cannot help it.

	       In multithreaded scripts Perl coordinates the threads so that
	       any thread may modify its copy of the $0 and the change becomes
	       visible to ps(1) (assuming the operating system plays along).
	       Note that the view of $0 the other threads have will not change
	       since they have their own copies of it.

       $[      The index of the first element in an array, and of the first
	       character in a substring.  Default is 0, but you could theoret
	       ically set it to 1 to make Perl behave more like awk (or For
	       tran) when subscripting and when evaluating the index() and
	       substr() functions.  (Mnemonic: [ begins subscripts.)

	       As of release 5 of Perl, assignment to $[ is treated as a com
	       piler directive, and cannot influence the behavior of any other
	       file.  (Thats why you can only assign compile-time constants
	       to it.)	Its use is highly discouraged.

	       Note that, unlike other compile-time directives (such as
	       strict), assignment to $[ can be seen from outer lexical scopes
	       in the same file.  However, you can use local() on it to
	       strictly bind its value to a lexical block.

       $]      The version + patchlevel / 1000 of the Perl interpreter.  This
	       variable can be used to determine whether the Perl interpreter
	       executing a script is in the right range of versions.
	       (Mnemonic: Is this version of perl in the right bracket?)

		   warn "No checksumming!\n" if $] < 3.019;

	       See also the documentation of "use VERSION" and "require VER
	       SION" for a convenient way to fail if the running Perl inter
	       preter is too old.

	       When testing the variable, to steer clear of floating point
	       inaccuracies you might want to prefer the inequality tests "<"
	       and ">" to the tests containing equivalence: "<=", "==", and

	       The floating point representation can sometimes lead to inaccu
	       rate numeric comparisons.  See $^V for a more modern represen
	       tation of the Perl version that allows accurate string compar

       $^C     The current value of the flag associated with the -c switch.
	       Mainly of use with -MO=... to allow code to alter its behavior
	       when being compiled, such as for example to AUTOLOAD at compile
	       time rather than normal, deferred loading.  See perlcc.	Set
	       ting "$^C = 1" is similar to calling "B::minus_c".

       $^D     The current value of the debugging flags.  (Mnemonic: value of
	       -D switch.) May be read or set. Like its command-line
	       equivalent, you can use numeric or symbolic values, eg "$^D =
	       10" or "$^D = "st"".

       $^F     The maximum system file descriptor, ordinarily 2.  System file
	       descriptors are passed to exec()ed processes, while higher file
	       descriptors are not.  Also, during an open(), system file
	       descriptors are preserved even if the open() fails.  (Ordinary
	       file descriptors are closed before the open() is attempted.)
	       The close-on-exec status of a file descriptor will be decided
	       according to the value of $^F when the corresponding file,
	       pipe, or socket was opened, not the time of the exec().

       $^H     WARNING: This variable is strictly for internal use only.  Its
	       availability, behavior, and contents are subject to change
	       without notice.

	       This variable contains compile-time hints for the Perl inter
	       preter.	At the end of compilation of a BLOCK the value of this
	       variable is restored to the value when the interpreter started
	       to compile the BLOCK.

	       When perl begins to parse any block construct that provides a
	       lexical scope (e.g., eval body, required file, subroutine body,
	       loop body, or conditional block), the existing value of $^H is
	       saved, but its value is left unchanged.	When the compilation
	       of the block is completed, it regains the saved value.  Between
	       the points where its value is saved and restored, code that
	       executes within BEGIN blocks is free to change the value of

	       This behavior provides the semantic of lexical scoping, and is
	       used in, for instance, the "use strict" pragma.

	       The contents should be an integer; different bits of it are
	       used for different pragmatic flags.  Heres an example:

		   sub add_100 { $^H |= 0x100 }

		   sub foo {
		       BEGIN { add_100() }

	       Consider what happens during execution of the BEGIN block.  At
	       this point the BEGIN block has already been compiled, but the
	       body of foo() is still being compiled.  The new value of $^H
	       will therefore be visible only while the body of foo() is being

	       Substitution of the above BEGIN block with:

		   BEGIN { require strict; strict->import(vars) }

	       demonstrates how "use strict vars" is implemented.  Heres a
	       conditional version of the same lexical pragma:

		   BEGIN { require strict; strict->import(vars) if $condition }

       %^H     WARNING: This variable is strictly for internal use only.  Its
	       availability, behavior, and contents are subject to change
	       without notice.

	       The %^H hash provides the same scoping semantic as $^H.	This
	       makes it useful for implementation of lexically scoped pragmas.

       $^I     The current value of the inplace-edit extension.  Use "undef"
	       to disable inplace editing.  (Mnemonic: value of -i switch.)

       $^M     By default, running out of memory is an untrappable, fatal
	       error.  However, if suitably built, Perl can use the contents
	       of $^M as an emergency memory pool after die()ing.  Suppose
	       that your Perl were compiled with "-DPERL_EMERGENCY_SBRK" and
	       used Perls malloc.  Then

		   $^M = a x (1 << 16);

	       would allocate a 64K buffer for use in an emergency.  See the
	       INSTALL file in the Perl distribution for information on how to
	       add custom C compilation flags when compiling perl.  To dis
	       courage casual use of this advanced feature, there is no
	       English long name for this variable.

       $^O     The name of the operating system under which this copy of Perl
	       was built, as determined during the configuration process.  The
	       value is identical to $Config{osname}.  See also Config and
	       the -V command-line switch documented in perlrun.

	       In Windows platforms, $^O is not very helpful: since it is
	       always "MSWin32", it doesnt tell the difference between
	       95/98/ME/NT/2000/XP/CE/.NET.  Use Win32::GetOSName() or
	       Win32::GetOSVersion() (see Win32 and perlport) to distinguish
	       between the variants.

	       An internal variable used by PerlIO.  A string in two parts,
	       separated by a "\0" byte, the first part describes the input
	       layers, the second part describes the output layers.

       $^P     The internal variable for debugging support.  The meanings of
	       the various bits are subject to change, but currently indicate:

	       0x01  Debug subroutine enter/exit.

	       0x02  Line-by-line debugging.

	       0x04  Switch off optimizations.

	       0x08  Preserve more data for future interactive inspections.

	       0x10  Keep info about source lines on which a subroutine is

	       0x20  Start with single-step on.

	       0x40  Use subroutine address instead of name when reporting.

	       0x80  Report "goto &subroutine" as well.

	       0x100 Provide informative "file" names for evals based on the
		     place they were compiled.

	       0x200 Provide informative names to anonymous subroutines based
		     on the place they were compiled.

	       0x400 Debug assertion subroutines enter/exit.

	       Some bits may be relevant at compile-time only, some at run-
	       time only.  This is a new mechanism and the details may change.

       $^R     The result of evaluation of the last successful "(?{ code })"
	       regular expression assertion (see perlre).  May be written to.

       $^S     Current state of the interpreter.

		   $^S	       State
		   ---------   -------------------
		   undef       Parsing module/eval
		   true (1)    Executing an eval
		   false (0)   Otherwise

	       The first state may happen in $SIG{__DIE__} and $SIG{__WARN__}

       $^T     The time at which the program began running, in seconds since
	       the epoch (beginning of 1970).  The values returned by the -M,
	       -A, and -C filetests are based on this value.

	       Reflects if taint mode is on or off.  1 for on (the program was
	       run with -T), 0 for off, -1 when only taint warnings are
	       enabled (i.e. with -t or -TU).

	       Reflects certain Unicode settings of Perl.  See perlrun docu
	       mentation for the "-C" switch for more information about the
	       possible values. This variable is set during Perl startup and
	       is thereafter read-only.

	       This variable indicates whether an UTF-8 locale was detected by
	       perl at startup. This information is used by perl when its in
	       adjust-utf8ness-to-locale mode (as when run with the "-CL" com
	       mand-line switch); see perlrun for more info on this.

       $^V     The revision, version, and subversion of the Perl interpreter,
	       represented as a string composed of characters with those ordi
	       nals.  Thus in Perl v5.6.0 it equals "chr(5) . chr(6) . chr(0)"
	       and will return true for "$^V eq v5.6.0".  Note that the char
	       acters in this string value can potentially be in Unicode

	       This can be used to determine whether the Perl interpreter exe
	       cuting a script is in the right range of versions.  (Mnemonic:
	       use ^V for Version Control.)  Example:

		   warn "No \"our\" declarations!\n" if $^V and $^V lt v5.6.0;

	       To convert $^V into its string representation use sprintf()s
	       "%vd" conversion:

		   printf "version is v%vd\n", $^V;  # Perls version

	       See the documentation of "use VERSION" and "require VERSION"
	       for a convenient way to fail if the running Perl interpreter is
	       too old.

	       See also $] for an older representation of the Perl version.

       $^W     The current value of the warning switch, initially true if -w
	       was used, false otherwise, but directly modifiable.  (Mnemonic:
	       related to the -w switch.)  See also warnings.

	       The current set of warning checks enabled by the "use warnings"
	       pragma.	See the documentation of "warnings" for more details.

       $^X     The name used to execute the current copy of Perl, from Cs
	       "argv[0]" or (where supported) /proc/self/exe.

	       Depending on the host operating system, the value of $^X may be
	       a relative or absolute pathname of the perl program file, or
	       may be the string used to invoke perl but not the pathname of
	       the perl program file.  Also, most operating systems permit
	       invoking programs that are not in the PATH environment vari
	       able, so there is no guarantee that the value of $^X is in
	       PATH.  For VMS, the value may or may not include a version num

	       You usually can use the value of $^X to re-invoke an indepen
	       dent copy of the same perl that is currently running, e.g.,

		 @first_run = $^X -le "print int rand 100 for 1..100";

	       But recall that not all operating systems support forking or
	       capturing of the output of commands, so this complex statement
	       may not be portable.

	       It is not safe to use the value of $^X as a path name of a
	       file, as some operating systems that have a mandatory suffix on
	       executable files do not require use of the suffix when invoking
	       a command.  To convert the value of $^X to a path name, use the
	       following statements:

		 # Build up a set of file names (not command names).
		 use Config;
		 $this_perl = $^X;
		 if ($^O ne VMS)
		    {$this_perl .= $Config{_exe}
			 unless $this_perl =~ m/$Config{_exe}$/i;}

	       Because many operating systems permit anyone with read access
	       to the Perl program file to make a copy of it, patch the copy,
	       and then execute the copy, the security-conscious Perl program
	       mer should take care to invoke the installed copy of perl, not
	       the copy referenced by $^X.  The following statements accom
	       plish this goal, and produce a pathname that can be invoked as
	       a command or referenced as a file.

		 use Config;
		 $secure_perl_path = $Config{perlpath};
		 if ($^O ne VMS)
		    {$secure_perl_path .= $Config{_exe}
			 unless $secure_perl_path =~ m/$Config{_exe}$/i;}

       ARGV    The special filehandle that iterates over command-line file
	       names in @ARGV. Usually written as the null filehandle in the
	       angle operator "<>". Note that currently "ARGV" only has its
	       magical effect within the "<>" operator; elsewhere it is just a
	       plain filehandle corresponding to the last file opened by "<>".
	       In particular, passing "\*ARGV" as a parameter to a function
	       that expects a filehandle may not cause your function to auto
	       matically read the contents of all the files in @ARGV.

       $ARGV   contains the name of the current file when reading from <>.

       @ARGV   The array @ARGV contains the command-line arguments intended
	       for the script.	$#ARGV is generally the number of arguments
	       minus one, because $ARGV[0] is the first argument, not the pro
	       grams command name itself.  See $0 for the command name.

       ARGVOUT The special filehandle that points to the currently open output
	       file when doing edit-in-place processing with -i.  Useful when
	       you have to do a lot of inserting and dont want to keep modi
	       fying $_.  See perlrun for the -i switch.

       @F      The array @F contains the fields of each line read in when
	       autosplit mode is turned on.  See perlrun for the -a switch.
	       This array is package-specific, and must be declared or given a
	       full package name if not in package main when running under
	       "strict vars".

       @INC    The array @INC contains the list of places that the "do EXPR",
	       "require", or "use" constructs look for their library files.
	       It initially consists of the arguments to any -I command-line
	       switches, followed by the default Perl library, probably
	       /usr/local/lib/perl, followed by ".", to represent the current
	       directory.  ("." will not be appended if taint checks are
	       enabled, either by "-T" or by "-t".)  If you need to modify
	       this at runtime, you should use the "use lib" pragma to get the
	       machine-dependent library properly loaded also:

		   use lib /mypath/libdir/;
		   use SomeMod;

	       You can also insert hooks into the file inclusion system by
	       putting Perl code directly into @INC.  Those hooks may be sub
	       routine references, array references or blessed objects.  See
	       "require" in perlfunc for details.

       @_      Within a subroutine the array @_ contains the parameters passed
	       to that subroutine.  See perlsub.

       %INC    The hash %INC contains entries for each filename included via
	       the "do", "require", or "use" operators.  The key is the file
	       name you specified (with module names converted to pathnames),
	       and the value is the location of the file found.  The "require"
	       operator uses this hash to determine whether a particular file
	       has already been included.

	       If the file was loaded via a hook (e.g. a subroutine reference,
	       see "require" in perlfunc for a description of these hooks),
	       this hook is by default inserted into %INC in place of a file
	       name.  Note, however, that the hook may have set the %INC entry
	       by itself to provide some more specific info.

	       The hash %ENV contains your current environment.  Setting a
	       value in "ENV" changes the environment for any child processes
	       you subsequently fork() off.

	       The hash %SIG contains signal handlers for signals.  For exam

		   sub handler {       # 1st argument is signal name
		       my($sig) = @_;
		       print "Caught a SIG$sig--shutting down\n";

		   $SIG{INT}  = \&handler;
		   $SIG{QUIT} = \&handler;
		   $SIG{INT}  = DEFAULT;   # restore default action
		   $SIG{QUIT} = IGNORE;    # ignore SIGQUIT

	       Using a value of IGNORE usually has the effect of ignoring
	       the signal, except for the "CHLD" signal.  See perlipc for more
	       about this special case.

	       Here are some other examples:

		   $SIG{"PIPE"} = "Plumber";   # assumes main::Plumber (not recommended)
		   $SIG{"PIPE"} = \&Plumber;   # just fine; assume current Plumber
		   $SIG{"PIPE"} = *Plumber;    # somewhat esoteric
		   $SIG{"PIPE"} = Plumber();   # oops, what did Plumber() return??

	       Be sure not to use a bareword as the name of a signal handler,
	       lest you inadvertently call it.

	       If your system has the sigaction() function then signal han
	       dlers are installed using it.  This means you get reliable
	       signal handling.

	       The default delivery policy of signals changed in Perl 5.8.0
	       from immediate (also known as "unsafe") to deferred, also known
	       as "safe signals".  See perlipc for more information.

	       Certain internal hooks can be also set using the %SIG hash.
	       The routine indicated by $SIG{__WARN__} is called when a warn
	       ing message is about to be printed.  The warning message is
	       passed as the first argument.  The presence of a __WARN__ hook
	       causes the ordinary printing of warnings to STDERR to be sup
	       pressed.  You can use this to save warnings in a variable, or
	       turn warnings into fatal errors, like this:

		   local $SIG{__WARN__} = sub { die $_[0] };
		   eval $proggie;

	       The routine indicated by $SIG{__DIE__} is called when a fatal
	       exception is about to be thrown.  The error message is passed
	       as the first argument.  When a __DIE__ hook routine returns,
	       the exception processing continues as it would have in the
	       absence of the hook, unless the hook routine itself exits via a
	       "goto", a loop exit, or a die().  The "__DIE__" handler is
	       explicitly disabled during the call, so that you can die from a
	       "__DIE__" handler.  Similarly for "__WARN__".

	       Due to an implementation glitch, the $SIG{__DIE__} hook is
	       called even inside an eval().  Do not use this to rewrite a
	       pending exception in $@, or as a bizarre substitute for over
	       riding CORE::GLOBAL::die().  This strange action at a distance
	       may be fixed in a future release so that $SIG{__DIE__} is only
	       called if your program is about to exit, as was the original
	       intent.	Any other use is deprecated.

	       "__DIE__"/"__WARN__" handlers are very special in one respect:
	       they may be called to report (probable) errors found by the
	       parser.	In such a case the parser may be in inconsistent
	       state, so any attempt to evaluate Perl code from such a handler
	       will probably result in a segfault.  This means that warnings
	       or errors that result from parsing Perl should be used with
	       extreme caution, like this:

		   require Carp if defined $^S;
		   Carp::confess("Something wrong") if defined &Carp::confess;
		   die "Something wrong, but could not load Carp to give backtrace...
			To see backtrace try starting Perl with -MCarp switch";

	       Here the first line will load Carp unless it is the parser who
	       called the handler.  The second line will print backtrace and
	       die if Carp was available.  The third line will be executed
	       only if Carp was not available.

	       See "die" in perlfunc, "warn" in perlfunc, "eval" in perlfunc,
	       and warnings for additional information.

       Error Indicators

       The variables $@, $!, $^E, and $? contain information about different
       types of error conditions that may appear during execution of a Perl
       program.  The variables are shown ordered by the "distance" between the
       subsystem which reported the error and the Perl process.  They corre
       spond to errors detected by the Perl interpreter, C library, operating
       system, or an external program, respectively.

       To illustrate the differences between these variables, consider the
       following Perl expression, which uses a single-quoted string:

	   eval q{
	       open my $pipe, "/cdrom/install |" or die $!;
	       my @res = <$pipe>;
	       close $pipe or die "bad pipe: $?, $!";

       After execution of this statement all 4 variables may have been set.

       $@ is set if the string to be "eval"-ed did not compile (this may hap
       pen if "open" or "close" were imported with bad prototypes), or if Perl
       code executed during evaluation die()d .  In these cases the value of
       $@ is the compile error, or the argument to "die" (which will interpo
       late $! and $?).  (See also Fatal, though.)

       When the eval() expression above is executed, open(), "", and
       "close" are translated to calls in the C run-time library and thence to
       the operating system kernel.  $! is set to the C librarys "errno" if
       one of these calls fails.

       Under a few operating systems, $^E may contain a more verbose error
       indicator, such as in this case, "CDROM tray not closed."  Systems that
       do not support extended error messages leave $^E the same as $!.

       Finally, $? may be set to non-0 value if the external program
       /cdrom/install fails.  The upper eight bits reflect specific error con
       ditions encountered by the program (the programs exit() value).	 The
       lower eight bits reflect mode of failure, like signal death and core
       dump information  See wait(2) for details.  In contrast to $! and $^E,
       which are set only if error condition is detected, the variable $? is
       set on each "wait" or pipe "close", overwriting the old value.  This is
       more like $@, which on every eval() is always set on failure and
       cleared on success.

       For more details, see the individual descriptions at $@, $!, $^E, and

       Technical Note on the Syntax of Variable Names

       Variable names in Perl can have several formats.  Usually, they must
       begin with a letter or underscore, in which case they can be arbitrar
       ily long (up to an internal limit of 251 characters) and may contain
       letters, digits, underscores, or the special sequence "::" or "".  In
       this case, the part before the last "::" or "" is taken to be a pack
       age qualifier; see perlmod.

       Perl variable names may also be a sequence of digits or a single punc
       tuation or control character.  These names are all reserved for special
       uses by Perl; for example, the all-digits names are used to hold data
       captured by backreferences after a regular expression match.  Perl has
       a special syntax for the single-control-character names: It understands
       "^X" (caret "X") to mean the control-"X" character.  For example, the
       notation $^W (dollar-sign caret "W") is the scalar variable whose name
       is the single character control-"W".  This is better than typing a lit
       eral control-"W" into your program.

       Finally, new in Perl 5.6, Perl variable names may be alphanumeric
       strings that begin with control characters (or better yet, a caret).
       These variables must be written in the form "${^Foo}"; the braces are
       not optional.  "${^Foo}" denotes the scalar variable whose name is a
       control-"F" followed by two "o"s.  These variables are reserved for
       future special uses by Perl, except for the ones that begin with "^_"
       (control-underscore or caret-underscore).  No control-character name
       that begins with "^_" will acquire a special meaning in any future ver
       sion of Perl; such names may therefore be used safely in programs.  $^_
       itself, however, is reserved.

       Perl identifiers that begin with digits, control characters, or punctu
       ation characters are exempt from the effects of the "package" declara
       tion and are always forced to be in package "main"; they are also
       exempt from "strict vars" errors.  A few other names are also exempt
       in these ways:

	       ENV	       STDIN
	       INC	       STDOUT
	       ARGV	       STDERR
	       ARGVOUT	       _

       In particular, the new special "${^_XYZ}" variables are always taken to
       be in package "main", regardless of any "package" declarations
       presently in scope.

       Due to an unfortunate accident of Perls implementation, "use English"
       imposes a considerable performance penalty on all regular expression
       matches in a program, regardless of whether they occur in the scope of
       "use English".  For that reason, saying "use English" in libraries is
       strongly discouraged.  See the Devel::SawAmpersand module documentation
       from CPAN ( http://www.cpan.org/modules/by-module/Devel/ ) for more

       Having to even think about the $^S variable in your exception handlers
       is simply wrong.  $SIG{__DIE__} as currently implemented invites
       grievous and difficult to track down errors.  Avoid it and use an
       "END{}" or CORE::GLOBAL::die override instead.

perl v5.8.8			  2008-04-25			    PERLVAR(1)

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